Magnus Olafsson (Old Norse: Magnús Óláfsson, Norwegian: Magnus Olavsson; 1073 – 24 August 1103), better known as Magnus Barefoot (Old Norse: Magnús berfœttr, Norwegian: Magnus Berrføtt), was King of Norway (as Magnus III) from 1093 until his death in 1103. His reign was marked by aggressive military campaigns and conquest, particularly in the Norse-dominated parts of the British Isles, and he extended his rule to the Kingdom of the Isles and Dublin.

As the only son of King Olaf Kyrre, Magnus was proclaimed king in southeastern Norway shortly after his father's death in 1093. In the north his claim was contested by his cousin, Haakon Magnusson (son of King Magnus Haraldsson), and the two co-ruled uneasily until Haakon's death in 1095. Disgruntled members of the nobility refused to recognise Magnus after his cousin's death, but the insurrection was short-lived. After securing his position domestically, Magnus campaigned around the Irish Sea from 1098 to 1099. He raided through Orkney, the Hebrides and Mann (the Northern and Southern Isles), and ensured Norwegian control by a treaty with the Scottish king. Based on Mann during his time in the west, Magnus had a number of forts and houses built on the island and probably also obtained suzerainty of Galloway. He sailed to Wales later in his expedition, winning control of Anglesey (and possibly Gwynedd's submission) after repelling the invading Norman forces from the island.

Following his return to Norway Magnus led campaigns into Dalsland and Västergötland in Sweden, claiming an ancient border with the country. After two unsuccessful invasions and a number of skirmishes Danish king Eric Evergood initiated peace talks among the three Scandinavian monarchs, fearing that the conflict would get out of hand. Magnus concluded peace with the Swedes in 1101 by agreeing to marry Margaret, daughter of the Swedish king Inge Stenkilsson. In return, Magnus gained Dalsland as part of her dowry. He set out on his final western campaign in 1102, and may have sought to conquer Ireland. Magnus entered into an alliance with Irish king Muirchertach Ua Briain of Munster, who recognised Magnus' control of Dublin. Under unclear circumstances, while obtaining food supplies for his return to Norway, Magnus was killed in an ambush by the Ulaid the next year; territorial advances characterising his reign ended with his death.

Into modern times, his legacy has remained more pronounced in Ireland and Scotland than in his native Norway. Among the few domestic developments known during his reign, Norway developed a more-centralised rule and moved closer to the European model of church organisation. Popularly portrayed as a Viking warrior rather than a medieval monarch, Magnus was the last Norwegian king to fall in battle abroad, and he may in some respects be considered the final Viking king.[1]